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HIIT the Big Time

The case for high-intensity interval training cardio.

Greg Merritt

Edgar Artiga

Over at the rack, some HIT-man is screaming his way through a low-rep set of squats while his partners bark encouragement. Is his strategy of maximum effort and minimal volume the fastest route to muscle growth? It’s debatable. Most people who try a strict HIT system eventually answer no. But there is a place in the gym where high intensity rules. It’s not the power rack or, for that matter, anything to do with weights. Focus instead on everyone bouncing along on cardio contraptions. They should all be doing HIT, or, more precisely, HIIT. Maybe they should’ve psyched themselves up before stepping on that elliptical or StairMaster because high-intensity interval training is the best cardio strategy for incinerating body fat.

If you’ve played organized basket- ball, football, or soccer, you probably ran a lot of wind sprints, which alternate periods of sprinting with periods of walking. Wind sprints are a form of high-intensity interval training. Whether performed on a track, in a pool, or on a cardio machine, HIIT prescribes a back and forth between high intensity and low or no intensity. Numerous studies have verified the effective- ness of HIIT, primarily because it elevates your metabolic rate for a longer period than less grueling but lengthier alternatives. For example, a 2007 study demonstrated that subjects who performed HIIT burned roughly 10% more calories in the 24 hours post-workout when compared with those who did cardio at a steady pace. Even more eye-opening was a 2008 study, in which subjects following a HIIT program of 20-minute ses- sions lost nearly six times the body fat of those doing a program of 40-minute lower-intensity cardio.

Let’s break down how to do HIIT. There will be math, so open a calculator app. First, determine your maximum heart rate by subtracting your age from 220. So, if you’re 25, your MHR is 195. High-intensity intervals should elevate your heart rate to 80–90% of your MHR. So that same 25-year-old should aim for 156 to 176 beats per minute. During the lower-intensity intervals, your heart rate should top no more than 60% of your MHR. Therefore, a 25-year-old should be at 117 or less. HIIT dovetails perfectly with wearable technology like Fitbit, which make it easy to moderate your heart and time your intervals. However, with experience you should be able to feel about how much exertion to do in both the high- and low-intensity intervals.

If this is your first time doing HIIT, begin with a 1-to-2 ratio of high to low intensity, 20 seconds of the former alternated with 40 seconds of the latter for 10 of each. Over eight weeks, gradually increase the length of the high-intensity intervals and decrease the lengths of the low-intensity intervals. Ideally, you’ll want to be at 30/30 at four weeks and 40/20 at eight weeks. Getting to a 2-to-1 ratio is dependent on your fitness levels, how hard you push both intervals, and how many intervals you do. You don’t necessarily have to stick to 2-to-1 long term. To boost fat torching, you can lengthen both intervals, and you can add intervals, up to 20 of each. Our sample routine has a 40/30 split with 15 of each.

When it comes to which cardio exercise to do, select something strenuous enough to elevate your heart rate sufficiently. That prob- ably eliminates the recumbent bike. The best machines for this are the hard ones—the StepMill, the elliptical, and the stepper—though a treadmill or stationary bike will also work if you push your pace fast enough. You may want to combine two machines. For example, do your high-intensity intervals vigorously climbing a StepMill and your low-intensity intervals casually strolling on a treadmill. Outdoors, the aforementioned wind sprints are a great option. And at home or in a hotel room, you can do bur- pees. Try alternating 10 burpees with 20 to 30 seconds of shadow boxing and build up to 10 of each.

HIIT sessions are short. Our sample workout is over in less than 18 minutes, and even the lengthiest HIIT workout should clock out at less than a half-hour. This is usually an advantage, but not always. Some of us use cardio to clear our head with an hour-long morning jog or to enjoy a 50-minute podcast on a stationary bike after a battle of man versus metal. If you choose to do longer, less-intense cardio, you should still incorporate some higher-intensity work. For example, sprint 200 yards a few times during that jog, and pedal as fast as you can for 40 seconds a few times during that stationary bike ride. Intensity has been proven to boost fat burning dramatically, so, whatever sort of cardio you do, make certain you crank up the pace at least some of the time every time.